Method and use of a stretchable nonreinforced tpo building materials

ABSTRACT

In one embodiment, the present invention relates to a membrane for use as an outdoor building material comprising a non-reinforced TPO outdoor building material membrane composed of a single ply embossed thermoplastic polyolefin polymer wherein the embossed membrane has a stretchability in the range of about 5 lbf to about 30 lbf, as tested with about a 30-mil thickness sample under the “stretchability test.” In yet another embodiment, the present invention relates to a method of applying a non-reinforced TPO outdoor building material membrane to a motor home roof comprising the step of: a) applying a non-reinforced TPO membrane to RV roof wood deck, wherein the membrane is composed of a thermoplastic polyolefin polymer with at least one of the following ingredients of a fire retardant, a UV and thermal stabilizers, a titanium dioxide and a calcium carbonate and wherein the membrane has a stretchability in the range of about 5 lbf to about 30 lbf, as tested with about a 30-mil thickness sample under the “stretchability test” and wherein the roofing membrane has a whiteness of at least an L* value of 90 as measured by the Whiteness Test; and b) adhering the non-reinforced TPO membrane to the wood deck via factory or field applied adhesive with a minimum 4 PLI of peel strength under the ASTM D413 peel test.

FIELD OF THE INVENTION

In one embodiment, the present invention relates to outdoor buildingmaterial (e.g. building materials roofing membrane, signage, awnings,wall coverage, and cover tapes) and in one specific embodiment, to anon-reinforced elastomeric TPO outdoor building material membrane thatexhibits substantially equivalent stretchable properties as ethylenepropylene diene monomer (“EPDM”).

BACKGROUND OF THE INVENTION

A typical low-slope roofing system consists of three components: astructural deck, a thermal insulation barrier and a waterproofingmembrane, which consists of reinforcing fibers or fabric sandwichedbetween two sheets of flexible matrix. The matrix material is eitherasphalt- or polymer-based. There are essentially two classes ofpolymer-based roofing membranes: thermosets and thermoplastics.Thermoplastics reversibly soften when heated, whereas thermosets do not.Thermoplastics encompass thermoplastic polyolefins (TPOs).

A typical TPO is a melt blend or reactor blend of a polyolefin plastic,typically a polypropylene polymer, with an olefin copolymer elastomer(OCE), typically an ethylene-propylene rubber (EPR) or anethylene-propylene-diene rubber (EPDR). Conventionally, a suitableroofing membrane exhibits the following properties: sufficiently strongenough to withstand stresses and to accommodate deck movement. Examplesof commercially available TPO membranes include SURE WELD™ (CarlisleInc.), GENFLEX™ (Omnova Solutions, Inc), ULTRAPLY™ (Firestone BuildingProducts) and EVERGUARD TPO™ (OAF). Typically, these membranes are fixedover a roof having insulation material placed thereon.

Problems with these membranes are that they have a rigid feel, tend tohold their shape, and do not relax quickly. The stiffnesscharacteristics affect the membrane installation process. As such, theyare generally not pliable to conform to the shape of detailing profiles(e.g. around HVAC and skyline windows) where detailing works arerequired for waterproofing.

Conventional reinforced TPO membranes are manufactured with areinforcing scrim encapsulated between two layers of TPO compounds. Inone example, the TPO sheet is reinforced with a polyester fleecereinforcement layer. Two TPO membranes are typically sealed by hot airheat-welding or seamed together using an adhesive. The hot air melts thepolymer at the seam and the two strips of membrane become fused andbonded with gentle pressure. Another desirable characteristic of TPOmembranes is the high heat seal strength. There are two sets of forcesconstantly working to damage the roofing seams. Wind uplift attempts topeel the seams apart. Building movement attempts to pull the seamsapart. High seal strength provides high wind resistance for the roof andlong life waterproofing. A conventional Ziegler-Natta catalyzed TPO hasa bimodal or broad molecular weight distribution. The low molecularweight oligomers migrate to membrane surface preventing welding ordeteriorating the heat seam strength. A TPO with a narrow molecularweight distribution eliminates surface blooming and provides high heatseal peel strength.

In contrast, ethylene propylene diene monomer (or terpolymer which issimply a product consisting of three distinct monomers) (“EPDM”) hasbeen in use on roofs in the USA since the 1960's and is one of the mostcommon types of low-slope roofing materials. This is because it isrelatively inexpensive, simple to install, and fairly clean to work withwhen compared to conventional built-up roofs. In addition, due to itssuperior stretchability to conform to roof corners and angle changes,Nonreinforced EPDM is widely used as a roof covering for most motorhomes and recreational vehicles. In one specific application, TiO₂ isadded to produce a white EPDM. However, compared to white TPO, whiteEPDM typically does not stand up to the weather because it caulks, losesits color, shrinks and does not lay flat.

EPDM roofs are typically single-ply membranes either a singlenonreinforced EPDM layer or a sandwich of top, bottom TPO layers and areinforcement within. EPDM is classified as a thermoset material whichmeans it is either fully-cured prior to being installed or that it curesduring natural weathering after installation. EPDM is a rubber materialwhose principal components consist of the compounds ethylene andpropylene. A flexible rubber matrix forms when a small amount of dieneis added to the mix. EPDM is available reinforced or unreinforced withboth commonly used; it's also available in either a cured (vulcanized)or uncured (non-vulcanized) state. Vulcanized EPDM is the most commonwith non-vulcanized often used for flashing purposes.

SUMMARY OF THE INVENTION

In one embodiment, the present invention is a membrane for use as anoutdoor building material comprising a non-reinforced TPO outdoorbuilding material membrane composed of a single ply embossedthermoplastic polyolefin polymer wherein the embossed membrane exhibitssubstantially equivalent stretchable properties as ethylene propylenediene monomer (“EPDM”).

TPO elastomer of the present invention is a thermoplastic polyolefinthat is a polypropylene based copolymer with less than about 25% (on aweight basis) of polyethylene composition. Conventional TPO elastomer isa polyethylene based copolymer with more than 50% (on a weight basis) ofpolyethylene such as metallocene polyethylene (Dow Engage®, ExxonmobileExact®), and ethylene propylene rubber with 0% unsaturation (EPM).

In one embodiment, the present invention relates to an outdoor buildingmaterial composed of a non-reinforced TPO membrane wherein the embossedmembrane has a stretchability in the range of about 5 lbf to about 30lbf, as tested with about a 30-mil thickness sample under the“stretchability test.” In another embodiment, the non-reinforced TPOmembrane has a stretchability in the range of about 10 lbf to about 20lbf, as tested with about a 30-mil thickness sample under the“stretchability test.” In yet another embodiment, the embossedthermoplastic polyolefin polymer is a polypropylene base copolymer. In afurther embodiment, the embossed thermoplastic has a whiteness of atleast an L* value of 90 as measured by the Whiteness Test, disclosedherein.

In another embodiment, the present invention relates to a method ofproducing a non-reinforced TPO membrane comprising the steps of: mixinga thermoplastic polyolefin polymer with at least one of the followingingredients of a fire retardant, a UV and thermal stabilizers, atitanium dioxide and a calcium carbonate; extruding through a sheet dieto a thicknesses of about 15 to about 50 mils; and embossing theextruded material to a thickness of about 3 to about 15 mils to form asingle ply roofing membrane, wherein the embossed single ply roofingmembrane has a stretchability in the range of about 5 lbf to about 25lbf, as tested with about a 30-mil thickness sample under the“stretchability test.” In yet another embodiment, the thermoplasticpolyolefin polymer is mixed with at least the UV and thermalstabilizers, titanium dioxide and calcium carbonate. In a furtherembodiment, the embossed thermoplastic polyolefin polymer is apolypropylene base copolymer. In yet another embodiment, the embossedthermoplastic has a whiteness of at least an L* value of 90 as measuredby the Whiteness Test.

In yet another embodiment, the present invention relates to using thenon-reinforced TPO membrane of the present invention to an RV roof wooddeck, comprising the steps of: applying an adhesive to the wood deck;pulling the non-reinforced TPO membrane over the entire roof in onecontinuous piece, wherein the membrane is composed of a thermoplasticpolyolefin polymer with at least one of the following ingredients of afire retardant, a UV and thermal stabilizers, a titanium dioxide and acalcium carbonate and wherein the membrane has a stretchability in therange of about 5 lbf to about 30 lbf, as tested with about a 30-milthickness sample under the “stretchability test” and wherein the roofingmembrane has a whiteness of at least an L* value of 90 as measured bythe Whiteness Test; cutting the membrane in an X pattern for at leastopenings on a top of the RV root brooming the membrane; and securingedges of the membrane.

DETAILED DESCRIPTION OF THE INVENTION

Detailed embodiments of the present invention are disclosed herein;however, it is to be understood that the disclosed embodiments aremerely illustrative of the invention that may be embodied in variousforms. In addition, each of the examples given in connection with thevarious embodiments of the invention are intended to be illustrative,and not restrictive. Further, the figures are not necessarily to scale,some features may be exaggerated to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

In one embodiment, the present invention relates to a non-reinforced TPOmembrane made by a polypropylene based elastomer (PBE) that exhibitssubstantially equivalent stretchable properties as ethylene propylenediene monomer (“EPDM”) but, in contrast to EPDM, provides superior heatweldability, solar reflectivity, color fastness and substantially nocaulking. In one embodiment, the “stretchability” properties of thepresent invention is in the range of about 5 lbf to about 25 lbf, moreparticularly, from about 10 lbf to about 15 lbf as tested with about a30-mil thickness sample under ASTM D751 breaking test procedure asdetailed below for the “stretchability test.”

In addition, in yet another embodiment, the present invention relates tonon-reinforced TPO membrane made by a polypropylene base elastomer (PBE)that exhibits a superior whiteness—whiteness of at least an L* value of90 as measured by the Whiteness Test.

In one embodiment, the PBE polymer composition of the present inventionis propylene/alpha-olefin copolymers with semi-crystalline isotacticpropylene segments. In one specific embodiment, the PBE for use in thepresent invention have a comonomer range of between about5-15%>preferably about −15%. The comonomers are alpha-olefins. Inaddition, in another example, the PBE polymers have a narrow molecularweight distribution of 2-3. The molecular weight distribution isindicated by M_(w)/M_(n) (also referred to as polydispersity index or“PDI” or “MWD”).

In yet another embodiment, suitable TPO for use in the present inventionis Dow “Versify” (e.g. DE2300 and/or DE 2400).

For purposes of the present invention, the term “non-reinforced TPO”membrane means a single layer of TPO without a reinforced scrim or maton the back of the membrane. For purpose of the present invention, theterm “heat-sealable” means a_material that is capable of being joined bya heating method so as to create a molecular bonding at joints.

In yet another embodiment, suitable TPO for use in the present inventionis ExxonMobile “Vistamaxx” (e.g. 1100 and/or 6100). One method ofproducing such a TPO is disclosed in U.S. Pat. No. 6,927,258, which isincorporated by reference herein. For example, such a TPO is produced byblending a “first polymer component” (“FPC”) which is a predominatelycrystalline stereoregular polypropylene with a “second polymercomponent” (“SPC”) which is a crystallizable copolymer of a C2, C4-C20alpha.-olefin and propylene. Optional components of the blend are SPC2,a crystallizable copolymer of a C.sub.2, C.sub.4-C.sub.20 .alpha.-olefin(preferably ethylene), and process oil. Other optional components arefillers, colorants, antioxidants, nucleators and flow improvers.

The FPC melts higher than 110.degree. C. and has a heat of fusion of atleast 75 J/g, as determined by DSC analysis. The crystallinepolypropylene can be either homopolymer or copolymers with other alphaolefins. The SPC and the SPC2, if used, have stereoregular propylenesequences long enough to crystallize. The SPC has a melting point ofless than 105.degree. C. and has a heat of fusion of less than 75 J/g.The SPC2 has a melting point of less than 115.degree. C. and has a heatof fusion of less than 75 J/g. One embodiment is blending isotacticpolypropylene (FPC) with ethylene propylene copolymers (SPC) havingabout 4 wt. % to about 35 wt. % ethylene (to ensure high compatibilitywith the FPC). Both the FPC and the SPC have isotactic propylenesequences long enough to crystallize. The ratio of the FPC to the SPC ofthe blend composition may vary in the range of 1:99 to 95:5 by weightand, in particular, in the range 2:98 to 70:30 by weight.

In one embodiment, the propylene based elastomers of the presentinvention have a glass transition temperature (T. _(g)) range of about−25 to −35.degree. C. The T. _(g) as used herein is the temperatureabove which a polymer becomes soft and pliable, and below which itbecomes hard and glassy. The propylene based plastomers and elastomersof the present invention have a MFR range measured at 230° C. of betweenabout 0.5 to about 25, preferably about 2, and a melt temperature rangeof about 50 to 120° C.

In one embodiment, the propylene based elastomers of the presentinvention have a preferred shore A hardness range of about 60 to about90. However, it is understood that the shore A hardness range can bebelow 60

In one embodiment, the propylene based elastomers of the presentinvention have a flexural modulus range of about 500 to about 6000 Psi,preferably about 1500-5000 Psi.

In yet another embodiment, the TPO membrane of the present inventionincludes one or more of the following advantages over standard EPDMincluding the ability to stand up to the weather and thus, notsubstantially caulk, lose its color, shrink and/or lay flat.

In one embodiment, the TPO membranes of the present invention have athicknesses of about 15 to about 50 mils, and more particularly fromabout 25 to about 40 mils.

Suitable ingredients in addition to polymers in the non-reinforced TPOmembrane include, but are not limited to: fillers, color pigments, fireretardants, antioxidants, UV and thermal stabilizers and/or processingaids. Suitable ranges of the above ingredients include, but are notlimited 100 parts of highly stretchable polypropylene based elastomer,0-80 parts of fire retardant, 0-5 parts UV and thermal stabilizers, 5-10parts titanium dioxide and 0-80 parts calcium carbonate.

In yet another embodiment, the TPO membranes of the present inventionmay be any color such as white, grey, or beige. It may also havepredetermined printed or embossed designs on its top surface.

In another embodiment, suitable methods of producing the TPO polymers ofthe present invention include, but are not limited to, precompounding orby in-situ compounding using polymer-manufacturing processes such asBanbury mixing or twin screw extrusion. After further mixing with otheradditives, these TPO polymers are then formed into roofing materials.

In another embodiment, the building materials of the present inventioncan be applied for outdoor weathering applications such as signage,awnings, wall coverage, roofing accessories, detailing, flashingmembranes, T-joint patches, repair and cover tapes.

In yet another embodiment, the roofing membrane of the present inventionmay be fixed over the base roofing by any means known in the art such asvia factory or field applied butyl adhesive, water and solvent basedadhesive material, ballasted material, spot bonding, or mechanicalfastening.

The present invention is explained in greater detail by reference to thefollowing illustrative examples, but the present invention should not beconstrued as limited thereto.

EXAMPLES

The following illustrative examples employ the “stretchability test”:

-   -   1. Cut TPO samples (6″ by 4″) to test for breaking strength        according to Breaking Strength Procedure A-Grab Test Method        under ASTM D751-98.    -   2. Calibrate the Load Cell    -   3. Place the specimen symmetrically between two clamps of an        Instron machine with the longer dimension parallel to and the        shorter dimension at right angles to the direction of        application of the force. The distance between two clamps on TPO        membrane is 3 inches.    -   4. Start the Instron machine which shall be adjusted so that the        pulling clamp has a uniform speed of 12±0.5 inch/min.    -   5. Record the force (in pounds-force) to stretch the TPO        membrane for 1″ (i.e. at 4 inch of the distance between two        clamps).    -   6 The stretch ability is reported by the average of five        individual test results in procedure 5.

The following illustrative examples employ the “whiteness measurement”:

-   -   1. Configure your software to read using the desired color        scale, illuminant, and observer-C.I.E. (Commission International        d'Eclairage) color system at D65/10′ of illuminant/Observer        conditions.    -   2. Standardize the instrument in Reflectance-Specular Included        mode for the largest area of view possible for which the sample        can completely cover the hole in the port plate (preferably        LAV). First standardize on the light trap, then the white tile.    -   3. Center the sample to be measured over the reflectance port        and hold it in place using the sample clamp. Make sure that the        area of the sample to be measured faces the port and completely        covers the port.    -   4. Take a single color reading of the sample. Rotate the sample        90° and read it at least once more. Average the multiple color        readings for a single color measurement representing its color.        Averaging multiple readings with rotation between readings        minimizes measurement variation associated with directionality.    -   5. Record the average L* color values as the whiteness value.

Example Conventional Reinforced TPO

A standard single ply RV thermoplastic polyolefin (TPO) white roofingmembranes was made of 100 parts of reaction grade polypropylenecopolymers CA10A from Basell Polyolefins, and other ingredients, such as0-80 parts of fire retardant, 0-5 parts UV and thermal stabilizers, 5-10parts titanium dioxide and 0-80 parts calcium carbonate. The ingredientswere mixed in an extruder at 200° C. and extruded through a sheet die toa thickness of about 15-50 mils. A reinforcement polyester fleece fabricwas inserted on bottom sheets, and the two layers were pressed and TPOsheet was embossed into a 30-100 mil fleece back single ply membrane.The standard membrane then was tested for the stretch ability and otherproperties. Due to the reinforcement backing, the membrane had a verypoor stretchability—70 under the “stretchability test as illustrated inTable 1.

Example Conventional Non-Reinforced TPO

A standard single ply RV thermoplastic polyolefin (TPO) white roofingmembranes was made of 100 parts of reaction grade polypropylenecopolymers Basell Polyolefins, and other ingredients, such as 0-80 partsof fire retardant, 0-5 parts UV and thermal stabilizers, 5-10 partstitanium dioxide and 0-80 parts calcium carbonate. The ingredients weremixed in an extruder at 200° C. and extruded through a sheet die to athickness of about 15-50 mils. The standard membrane then was tested forthe stretch ability and other properties. As illustrated in Table 1, themembrane had a poor stretchability—52 under the “stretchability test.

Example Conventional PE Elastomer

100 parts of Engage 8200 of metallocence polyethylene-octene elastomermade by Dow Chemicals were mixed in an extruder at about 180° C. withthe same ingredients as described in the Standard Example above. Then,the mixture was extruded through a sheet die to thicknesses of about15-50 mils. The extrusion die width was from 96″ to 120″. The resultingextruded sheet was embossed via an embossing roll. The embossing wasabout 3 to about 15 mils. The membrane was tested for stretch abilityand other properties. As illustrated in Table 1, the membrane had a fairstretchability—18.5 under the “stretchability test.

Example 1-3

TPO Polymers as disclosed in Table 1 Versify propylene based elastomermade by Dow Chemicals were mixed in an extruder at about 200° C. withthe same ingredients as described in the Standard Example above. Then,the mixture was extruded through a sheet die to thicknesses of about15-50 mils. The extrusion die width was from 96″ to 120″. The resultingextruded sheet was embossed via an embossing roll. The embossing wasabout 3-15 mils. The membrane was tested for stretch ability and otherproperties. As illustrated in Table 1, the membrane had a superiorstretchability—under the “stretchability test.” In addition, themembrane exhibited a superior whiteness—whiteness of at least an L*value of 90 as measured by the Whiteness Test.

Those skilled in the art will readily observe that numerous modificationand alterations of the device may be made while retaining the teachingsof the invention. Accordingly, the above disclosure should be construedas limited only by the metes and bounds of the appended claims.

Example 4

100 parts of TPO polymer of Vistamaxx 6100 Polypropylene elastomer madeby ExxnonMobil Chemicals were mixed in an extruder at about 180° C. withthe same ingredients as described in the Standard Example above. Then,the mixture was extruded through a sheet die to thicknesses of about15-50 mils. The extrusion die width was from 96″ to 120″. The resultingextruded sheet was embossed via an embossing roll. The embossing wasabout 3 to about 15 mils. The membrane was tested for stretch abilityand other properties. As illustrated in Table 1, the membrane had asuperior stretchability—13 under the “stretchability test.” Although theconventional PE such as metallocene PE or linear low densitypolyethylene has the similar flexibility as the propylene basedelastomer of the present invention characterized by the flexuralmodulus, the compounded building materials of the present invention hadshown 40-50% superior stretchability than conventional polyethylenecompounds. In addition, the membrane exhibited a superiorwhiteness—whiteness of at least an L* value of 90 as measured by theWhiteness Test.

TABLE 1 RV Roofing Physical Property Comparison Conventional SingleConventional EPDM RV Ply TPO RV Flexible PE ASTM NonreinforcedReinforced* Nonreinforced Nonreinforced Polymers EPDM CA10A CA10A MPEFlex modulus (psi) D791 3400 12,000 12,000 1755 PE Content (%) 60–70 3535 78 Hardness, shore A D2240 64 90 90 70 Thickness D751 38 mils 32 mils25 mils 30-mil Force required to stretch the Modified 14 70 52 18.5membrane for 1″ CMD (Lbf) D751 Solar Reflectivity E903 60% 80% 80% 80%Whitness (L*) CIE 86 95 95 95 Heat weldability D413 NA NA ExcellentExcellent *25 mil standard single ply TPO sheet reinforced withpolyester fleece backing

RV Roofing Physical Property Comparison Ex. 3 Ex. 4 EX. 1 Ex. 2Invention 1 TPO Invention 2 TPO Nonreinforced NonreinforcedNonreinforced Nonreinforced Polymers 100% Versify 20% 2400/80% 2300 100%Versify DE Vistamaxx 6100 DE2300 2400 Flex modulus (psi) 4900 1700 1732PE Content (%) 12 15 16 Hardness, shore A 61 48 64 Thickness 30-mil30-mil 30–35 mil 30–35 mil Force required to stretch the 30 24 14 13membrane for 1″ CMD (Lbf) Solar Reflectivity 80% 80% 80% 80% Whitness(L*) 95 95 95 95 Heat weldability Excellent Excellent ExcellentExcellent *25 mil standard single ply TPO sheet reinforced withpolyester fleece backing

1-14. (canceled)
 15. A construction material, comprising a membranecomposed of at least a thermoplastic polyolefin-based material thatcomprises a polypropylene-based elastomer having a polyethylenecopolymer in an amount up to about 25 percent by weight.
 16. Theconstruction material of claim 15, wherein said material is an outdoorbuilding material.
 17. The outdoor building material of claim 16,wherein said polypropylene-based elastomer has a polyethylene copolymerin an amount in the range at about 12 percent to about 16 percent. 18.The outdoor building material of claim 16, wherein said membrane is anextruded membrane.
 19. The outdoor building material of claim 18,wherein said membrane is embossed with a pattern.
 20. The outdoorbuilding material of claim 19, wherein a sample of said embossedmembrane having a thickness of about 30 mil has a stretchability in therange of about 5 lbf to about 30 lbf, as measured by the stretchabilitytest.
 21. The outdoor building material of claim 20, wherein saidpattern has a thickness of about 3 mil to about 15 mil.
 22. The outdoorbuilding material of claim 16, wherein sad thermoplasticpolyolefin-based material comprises a blend of said polypropylene-basedelastomer with less than about 50 percent by weight of apolyethylene-based elastomer having a polyethylene copolymer in anamount of at least about 50 percent by weight.
 23. The outdoor buildingmaterial of claim 16, wherein said thermoplastic polyolefin-basedmaterial includes a fire retardant.
 24. The outdoor building material ofclaim 16, wherein said thermoplastic polyolefin-based material includesa UV stabilizer.
 25. The outdoor building material of claim 16, whereinsaid thermoplastic polyolefin-based material includes a thermalstabilizer.
 26. The outdoor building material of claim 16, wherein saidthermoplastic polyolefin-based material includes one or both of titaniumdioxide and calcium carbonate, and wherein said embossed membrane has awhiteness of at least an L* value of 90 as measured by the WhitenessTest.
 27. The outdoor building material of claim 26, wherein saidoutdoor building material is used to cover the root of a mobile home.28. The outdoor building material of claim 27, wherein said roofcomprises a wood deck, and said outdoor building material adheres tosaid wood deck via an adhesive with a minimum peel strength of 4 PLI asmeasured by the ASTM D413 peel test
 29. The outdoor building material ofclaim 26, wherein said outdoor building material is used for signage.30. The outdoor building material of claim 26, wherein said outdoorbuilding material is used for awnings.
 31. The construction material ofclaim 15, wherein said construction material is used for an automobileinterior panel.
 32. The construction material of claim 15, wherein saidconstruction material is used for an automobile seat cover.
 33. Animprovement to a method of producing a construction material comprisinga membrane, said improvement comprising the step of forming the membranefrom a thermoplastic polyolefin-based material comprising apolypropylene-based elastomer having a polyethylene copolymer in anamount up to about 25 percent.
 34. The improvement of claim 33, whereinsaid construction material is an outdoor building material.
 35. Theimprovement of claim 34, wherein said polypropylene-based elastomer hasa polyethylene component in an amount in the range of about 12 percentto about 16 percent.
 36. The improvement of claim 34, wherein saidforming step includes the step of extruding the thermoplasticpolyolefin-based material through a die.
 37. The improvement of claim36, wherein said forming step further includes the step of embossing apattern on the extruded material.
 38. The improvement of claim 37,wherein a sample of the embossed membrane having a thickness of about 30mil has a stretchability in the range of about 5 lbf to about 30 lbf, asmeasured by the “stretchability test.”
 39. The improvement of claim 38,wherein said pattern has a thickness of about 3 mil to about 15 mil. 40.The improvement of claim 34, wherein said improvement includes the stepof blending the polypropylene-based elastomer with less than about 50percent by weight of a polyethylene-based elastomer having apolyethylene copolymer in an amount of at least about 50 percent byweight, prior to said forming step.
 41. The improvement of claim 34,wherein said improvement includes the step of mixing the thermoplasticpolyolefin-based material with a fire retardant, prior to said formingstep.
 42. The method of claim 34, wherein said improvement includes thestep of mixing the thermoplastic polyolefin-based material with a UVstabilizer, prior to said forming step.
 43. The method of claim 34,wherein said improvement includes the step of mixing the thermoplasticpolyolefin-based material with a thermal stabilizer prior to saidforming step.
 44. The method of claim 34, wherein said improvementincludes the step of mixing the thermoplastic polyolefin-based materialwith one or both of titanium dioxide and calcium carbonate, prior tosaid forming step, such that the embossed membrane has a whiteness of atleast an L* value of 90 as measured by the whiteness test.